(a) Field of the Invention
This invention relates to an assembly for tapping of liquid metal from a metallurgical furnace and to an improved metallurgical furnace.
(b) Brief Description of the Prior Art
The Electric Arc Furnace is widely employed in steel production.
Initially the design of the Electric Arc Furnace was such that molten metal, especially steel was poured from the furnace, together with liquid slag into a ladle from a permanently open tapping hole or spout located above the slag line. Draining of the molten metal and liquid slag after each heat in the furnace necessitated tilting the furnace through an angle of 43.degree. to 45.degree. to the vertical.
A subsequent development was to employ a temporarily plugged tap hole above the slag line and effecting a discharge of the liquid slag through a separate outlet, before unplugging the tap hole for discharge of the molten metal. In general the same tilting angle was employed and some residual slag was entrained in the molten metal during the tapping.
It is increasingly desirable that the molten steel be tapped or poured from the furnace essentially free of the liquid slag formed in the furnace. Different systems have been developed in an attempt to achieve this. The most successful systems have been so-called Eccentric Bottom Tapping Systems. These systems employ a tap hole oriented vertically, through the extended bottom of the furnace hearth.
By consideration of the volume of molten metal which has a predetermined upper level in the furnace, and careful control of the amount discharged, an essentially slag-free discharge can be made completely below the slag line.
This vertical arrangement has, however, the particular disadvantage that it generally requires substantial modification to the furnace foundation, platform and ladle handling equipment.
Moreover, vertical orientation of the tap hole requires that work on the discharge side of the tap hole must be carried out under the furnace, which results in increased danger for operating and maintenance crews. Typically the tap hole has a temporary plug of refractory material which is sintered to form a solid plug. When the tap hole flap or door is opened the solid plug must be removed. The hazardous nature of the overhead work beneath the furnace is especially apparent when the solid plug does not fall clear of the tap hole when the tap hole flap or door is opened, and an oxygen lance or a rod is employed from below to clear the tap hole.
It is an object of this invention to avoid the dangers and disadvantages associated with the vertically oriented tap hole, while at the same time providing an essentially slag-free discharge of liquid metal.
It is a further object of this invention to provide an assembly for tapping of liquid metal from a furnace, whereby access to the tap hole can be readily and safely opened and closed.
It is still a further object of this invention to provide such an assembly including means for readily and safely displacing a temporary plug of refractory material from the tap hole, for discharge of liquid metal from the furnace.
It is yet another object of this invention to provide an improved metallurgical furnace, especially an Electric Arc Furnace, having an essentially horizontal tapping passage in the furnace wall below the slag line.